The present invention relates to a fill limiter for a liquid storage tank.
It is known practice for an underground or overground storage tank intended to contain a liquid to be fitted with a fill limiter, the function of which is to interrupt the filling of the tank when the liquid in the said tank reaches a predetermined level, so as to prevent overflow which would be harmful to the environment of the tank. This is especially sought after when the tank that is to be filled is located at a filling station delivering hydrocarbon fuels of various types.
Limiters with the simplest structure comprise a body, a valve mounted in the said body and able to move between an open position corresponding to the filling of the tank and a closed position corresponding to the interruption of the filling of the said tank; a float, connected to the said valve, accompanies the rise of the liquid in the tank so as to close the valve when the liquid in the tank reaches a predetermined level.
Numerous improvements have been made to limiters according to whether the storage tanks are fitted with manholes or inlet orifices for positioning limiters inside the storage tank.
In U.S. Pat. Nos. 1,289,490 and 1,689,066, limiters comprise a tube body equipped with an internal partition for delimiting two adjacent chambers placed side by side, one of the chambers acting as a passage for the liquid intended to fill the tank and the other housing a float which is connected to a valve capable of moving from an open position corresponding to a low liquid level in the tank, below the float, to a closed position corresponding to a high liquid level in the tank, the liquid still being below the shut-off valve. The re-opening of the valve in this prior art is still performed manually. What is more, and this is a serious disadvantage, there is no possibility of re-opening the valve when the official performing the filling operation does not interrupt filling while the valve is in the closed position.
Other limiters have recently been proposed. Such limiters are described, for example, in French Patent No. 89/16604, European Patent No. 0,312,320 and U.S. Pat. No. 4,667,711.
Each one of the limiters described in these patents comprises a float which is connected to the valve in such a way that as the liquid in the tank rises it is moved away from the body of the limiter. When the limiter is introduced into the tank inlet orifice, the float is housed at least partially in the body so as to reduce the size of the limiter.
However, such limiters, because the float travel is on the outside of the body, are not able to allow the tank to be completely filled. This is because it is necessary to keep a minimum space between the upper wall of the tank and the maximum raised position of the float.
FR-B-2,675,476 describes a fill limiter comprising a float moving vertically in a chamber formed in the body of the limiter, a valve which can move between a vertical open position and a horizontal closed position, the float being connected to the valve by means of a linkage which collaborates with a pawl for retaining the valve in the vertical open position, a deflector consisting of inclined blades being arranged above and a certain distance away from the valve. There is a return spring for returning the valve to the vertical open position when the force exerted by the column of liquid on the said valve is lower than the return force exerted by the spring.
The main drawback of this limiter lies in the complexity of the valve-operating means mounted between this valve and the float. What is more, it is necessary to precisely determine the distance separating the free end of the rod connected to the float from the pawl which catches on the valve. Now, too short a distance leads to untimely closure of the valve when the fluid has not reached the desired level in the tank; too great a distance leads to late closure of the valve.
Another drawback lies in the fact that it is necessary to design the valve return spring to be relatively weak so as to allow the valve to close for low deliveries of fluid, for example up to 15 m.sup.3. However, in this case, the re-opening of the valve becomes difficult because of the weakness of the return spring.